Nanocomposites of carbon nanotubes with polyaniline (PANI) constitute promising conducting nanomaterials, due to their ease of synthesis, electrical conductivity, and environmental stability. Variously shaped multi-walled carbon nanotube (MWCNT)-PANI nanocomposites were synthesized, and their electrical conductivities were compared. This study shows that new synthetic methods were able to control the shapes and electrical conductivities of MWCNT-PANI nanocomposites. The shapes of the MWCNT-PANI nanocomposites were changed by altering the reactant concentrations and the sequence of adding the initiator, ammonium persulfate (APS). The use of surface-modified MWCNTs instead of pristine MWCNTs is also an important factor determining the shapes of the nanocomposites. It was found that the electrical conductivity is strongly dependent on the shape and PANI content. The electrical conductivities of the MWCNT-PANI nanocomposites increased when the PANI/MWCNT ratio was decreased. The nanocomposites were characterized via field emission transmission electron microscopy (FE-TEM), Fourier-transform infrared (FT-IR) and ultraviolet-visible (UV-Vis) spectroscopy, and elementary analysis of the MWCNT-PANI nanocomposites.